The invention concerns a seal device for sealing off the area between a pump impeller and an adjacent non-rotating part.
In pumps with rotating impellers such as centrifugal pumps, the pumped medium is sucked into the center of the impeller and leaves at the circumference. It is then very important that the inlet part of the impeller is well fitted within the surrounding pump housing in order to prevent pumped medium from flowing back to the inlet. Such a back-flow, which is caused by the higher pressure within the pump housing, means losses and creation of turbulence in the inlet. In addition, pollutions may collect between pump impeller and pump housing inlet.
In order to obtain the necessary sealing between the impeller and non-rotating parts, it is common practice to arrange a wear part, for instance made of rubber, on the non-rotating part and let the impeller glide against that part during rotation. In this way an effective sealing is obtained as long as the wear part is intact. When pumping liquids containing pollutions such as sand, cloth plastic stripes, etc., there is a risk that the slot between seal ring and pump impeller becomes clogged which may cause expensive service work. As the pollutions restrain the rotation of the impeller, the energy consumption increases.
One way to solve the problem is to arrange a mechanical face seal between the impeller and the housing. By designing the sealing so that the seal slot becomes axially directed, quite a good sealing is obtained. A disadvantage is that this solution is comparatively expensive and in addition, considerable losses may occur.
Another way to solve the problem is to arrange a co-rotating O-ring on the impeller inlet part which is influenced by the pressure to glide against the non-rotating surface, the latter then being made of a different material. A relatively good sealing is obtained in this way, but one disadvantage is that the wear may be extensive causing short service intervals. It has also been noted that the O-ring has a tendency to lose its contact. If this occurs, the self-balancing ends and the seal does not function. This depends on the fact that dynamic forces caused by the O-ring are co-rotating.
Still another way to solve the problem is shown in EP-492 603 and U.S. Pat. Nos. 3,228,343 and 3,221,661. Here, the pump inlet is so designed that entering leakage flows are linked in a direction that shall decrease the disturbance of the main in flow.